Explosion-proof plug and receptacle with switch means



Oct. Z8, A APPLETOIN EXPLOSION-PROOF PLUG AND RECEPTACLE WITH SWITCH MEANS 5 Sheets-Sheet l Filed March '7, 1967 Filed March 7, 1967 A. I APPLETON Oct. 28, 1969 EXPLOSION-PROOF PLUG AND REGEPTACLE WITH SWITCH MEANS 5 Sheets-Sheet 2 INvENToP.

Ala-mun I. APPLeTaN Oct. 28, 1969 y A, l. APPLETQN 3,475,570

EXPLOSION-PROOF PLUG AND RECEPTACLE WITH SWITCH MEANS Filed March '7, 1967 5 Sheets-Sheet :5

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lNvEN-roe ARTHUR 1. APPLETQN @w/gL/QMJMJ; VWQCQMM Arrvs.

Oct. 28, 1969 A. l. APPLETON EXPLOSION-PROOF PLUG AND RECEFTACLE WITH SWITCH MEANS Filed March 7, 1967 5 Sheets-Sheet 4 INvaN'roR Ala-mue LAPPLEroN Oct. 28, 1969 A. APPLETON 3,475,570

EXPLOSION-PROOF PLUG AND RECEPTAGLE WITH SWITCH MEANS 5 Sheets-Sheet 5 Filed March 7, 1967 United States Patent O U.S. Cl. 20051.07 12 Claims ABSTRACT OF THE DISCLOSURE Electrical plug and receptacle adaptable for explosionproof use wherein the receptacle includes male contacts and the plug includes female contacts with a switching arrangement for opening and closing the circuit in the receptacle and provision is made for insuring that the exposed receptacle contacts are live only when the plug is inserted in the receptacle.

Electrical connector having a plurality of cooperating plug and receptacle contacts which includes provision for continued electric contact of neutral circuit members upon insertion of the plug into the receptacle.

An improved plug and receptacle with switching means having an improved retaining structure for preventing unauthorized removal of the plug from the receptacle.

The present invention relates generally to electrical connectors adaptable for use in highly explosive atmospheres. More particularly, the invention relates to improved explosion-proof plugs and receptacles of the type having open circuit contact members and incorporating a delayed action construction, so that electrical contact occurs subsequent to insertion and prior to withdrawal of the plug from the receptacle to avoid any likelihood of a chain type explosive reaction to the atmosphere.

There is disclosed and claimed in my copending application, Ser. No. 527,625, filed Dec. 2, 1965, for Explosion-Proof Plug and Receptacle With Switch Means, now U.S. Patent 3,330,920, July l1, 1967, an explosionproof electrical connector of the type with which the present invention is concerned wherein electrical contact between input contacts in the receptacle and output contacts in the plug is aected wholly within an explosion-proof housing and a rotatable snap acting contact arrangement is utilized whereby the electrical circuit therebetween iS open dun'ng insertion and withdrawal of the plug to insure that arcing will not occur before completely inserting or withdrawing the plug from the receptacle.

Accordingly, it is a primary aim of the present invention to provide an improved plug and receptacle structure adaptable to afording positive, safe and fool-proof protection in highly explosive atmospheres.

A further object of the present invention is to provide improved eelctrical connectors which utilize open circuit contacts during insertion and withdrawal of the plug from the receptacle, thereby insuring that arcing will not occur while separation exists between the plug and the receptacle.

Another object of the invention is to provide a plug and receptacle having an improved set of make and break contacts which provide a fast opening and closing of the circuit only when the plug and receptacle are in complete engagement with one another. In this connection, it is an object to provide an improved set of make and break contacts which are engaged and disengaged with a contacting action that not only insures an instantaneous completion or interruption of the circuit but which provides for insuring that smooth, dependable contacting surfaces are brought into engagement.

Still a further object of the invention is to provide a ice set of make and break contacts having the above features which are characterized by their reliability in operation, and by the fact that electrical contact will be maintained even over a great number of repeated openings and closings of the contacts. In this connection, it is an object to provide an explosion-proof connector having contact elements which assure a longer wearing life over repeated make and break actions.

It is another object of the present invention, in one aspect, to provide an improved plug and receptacle of the foregoing character which has provision for preventing unauthorized tampering with the connector. In this connection, it is an object of the present invention to provide an improved retaining structure for preventing unauthorized removal of the plug from the receptacle, yet which enables the plug to be locked to the receptacle but without preventing movement between an open contact and a closed contact position.

It is still a further object of the present invention to provide a connector adaptable for explosion-proof use which in addition to including open circuit contacts and delayed action means for insuring interruption of the circuit subsequent to insertion and prior to withdrawal of the plug from the receptacle, provides for continued electrical contact of neutral circuit members and the like upon insertion of the plug into the receptacle.

It is still a further object of the invention to provide an improved plug and receptacle with a switching arrangement which permits the use of male contacts on the receptacle, yet avoids any possibility that exposed live contacts will be present when the plug is not in the receptacle.

Other objects and advantages of the present invention will become apparent as the following description proceeds taken in conjunction with the accompanying drawings wherein:

FIGURE l is an elevation view, partly in section, of an exemplary explosion-proof plug and receptacle embodying the present invention, here showing the plug completely inserted in the receptacle;

FIG. la is a section view taken substantially in the plane of line liz-1a in FIG. l;

FIG. 2 is a front elevation view, with a portion cut away, of the receptacle shown in FIG. 1;

FIG. 3 is a side elevation view, slightly reduced, of a receptacle housing, here showing the plug restraining collar in an open position and including a protective cover in a closed position;

FIG. 4 is a front elevation view of a receptacle shown in FIG. 3;

FIG. 5V is a side elevation view of a plug embodynig the present invention, with a portion of the housing broken away;

FIG. 6 is a front end view of the plug depicted in FIG. 5;

FIG. 7 is a fragmentary view of a portion of the plug shown in FIG. 5, but here showing polarizing slots on the plug;

FIG. 8 is a fragmentary View of the receptacle of FIG. 1, with a portion of the housing broken away, but showing the receptacle with the plug removed;

FIGS. 9, 10, 11, and 12 are illustrative diagrams, in perspective, showing the positioning stages of the plug and receptacle contact members, respectively;

FIG. 13 is an elevation view partly in section illustrating a slightly modified form of a plug and receptacle embodying the features of the present invention; and

FIG. 14 is a view taken substantially along the line 14-14 in FIG. 13.

While the invention has been described in connection with certain preferred embodiments, it will be understood that I do not intend to be limited to the particular embodirnents illustrated. On the contrary, I intend to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Turning to the drawings, particularly FIG. 1, there is shown an illustrative electrical connector embodying the features of the present invention including a plug 14 and receptacle 16 engageable by the plug for coupling a plurality of conductors carried in cables 20 and 21 in a delayed action and an explosion-proof manner. Electrical connection between the plug 14 and the receptacle 16 is afforded by a plurality of connectors 22 on the plug engageable by a corresponding plurality of open circuit contact members 23 in the receptacle. In the illustrative connector, mechanical connection between the plug and receptacle is accomplished by fitting the plug within the receptacle and then rotating the plug relative to the receptacle to bring about delayed action electrical Contact.

Turning first to the plug 14 which carries the connectors 22, as shown in FIG. l, it comprises a tubular casing 26 having a sleeve-like extension 28 at the end adjacent the connectors 22. At the opposite end of the plug casing 26 there is provided a closure member, indicated generally at 29, which provides for gripping the plug when withdrawing it from or inserting it into the receptacle and which also contemplates the inclusion of cable gripping and sealing members.

As best viewed in FIG. 1, the closure member 29 is generally cup-shaped, one end being adapted to be threadably secured to the plug casing 26 and the other end including an axially extending bore 30 through which cable 21 extends. In order to grip the cable within the closure 29, a cable clamp is provided formed with a pair of opposed clamp members 32 (one being shown in FIG. 1) which are tightened together by bolts or the like. A sealing bushing 33 surrounding the cable within closure 29 formed of a resilient, compressible material, for example a suitable flexible compound such as neoprene rubber or the like is compressed into sealing relation with the cable and the closure 29 when the latter is attached to the plug housing 26. The compressing action brought about when securing closure 29 to the plug housing will squeeze the bushing 33` tightly into engagement with the outer sheath of the cable thereby effecting an explosion-proof and weatherproof seal effected to prevent the access of moisture, gases and the like to the interior of the plug where the contacts are located.

In carrying out the present invention, the plug connectors 22 are carried in an annular insulator block or disc 34 removably secured within the sleeve portion 28 of the plug casing 26 by bolts 35 or the like. For a similar purpose, a retaining member 35a may be fitted into an annular slot 36 formed in the inner peripheral wall of the sleeve portion 28 (FIGS. 5 and 6).

Referring to FIGS. l and 6, conjointly, the connectors 22 are female or socket members disposed proportionately about a central socket connector 38 in the block 34. It is one of the features of the present electrical connector that since the plug employs socket type contacts, a field coil can employ the same plugs at both ends thereby avoiding the disadvantage of having to hunt for proper plug ends for insertion into the receptacle.

For the purpose of connecting the connector 22 to the cable conductors in cable 21, reduced diameter shanks 39 on the connectors 22 project axially through block 34. Cylindrical sleeves 40 tting over the reduced Shanks 39 of the connectors 22 receive the conductor wires which are clamped fast to the shank 39 by threaded fastener 41 screwed into the sleeves 40. Similarly, the central connector 38 has a collar 42 fitting over its reduced shank portion 43 for receiving a wire from cable 21.

Turning now to the receptacle, the receptacle includes male type contacts 23 which are contained in a rotatable insulator disc 45 within a cylindrical sleeve-like body portion 46 having an annular mounting ange 50 for mounting the receptacle on a conduit box housing or the like, shown in phantom at 51.

In the illustrative embodiment shown in FIGS. l and 2, a collar 52 rotatably mounted on sleeve portion 46 of the receptacle carries a hinged cover which is provided for closing the open plug-receiving end of the receptacle (FIGS. 3 and 4). To this end, a pair of spaced ears 62 protruding from the collar 52 and provided with transverse apertures in which a pivot pin 64 is received hingeably supports cover 60'. A torque spring 61 is mounted on the hinge pin and biases cover 60 to a closed position against the end of the collar S2 (FIG. 3) thereby preventing the entrance of moisture or dirt into the receptacle when the plug has been removed.

In carrying out one of the important aspects of the present invention, contacts 23 of the receptacle are open circuit contacts to insure that arcing will not occur before completely inserting or withdrawing the plug from the receptacle. To accomplish this, referring to FIGS. l and 9, conjointly, each of the contacts 23 has secured thereto, axially extending lugs 23a which terminate in arcuate enlarged portions 23h which are generally kidney shaped in cross-section.

In order to open and close the circuit to the contacts 23, there is provided a plurality of bridging contact assemblies 66 carried by a rotatable disc 68 with the opposite ends of the assemblies extending outwardly on opposite sides of the disc 68. Each of the contact assemblies 66 comprises a pair of resilient contact elements 66a, 66b riveted or otherwise connected together and presenting slots 69, 70 adjacent opposite ends thereof. At least the end portions of the contacts 66a, 66b are arcuate so that the slots 69, 70 are also generally arcuate. Thus,

`slots 69, for example, receive corresponding arcuate end `portions 23h of contact lugs 23a, with the ends of contacts 66a, 66h defining slot 69 being normally urged inwardly to insure a more positive connection when end portions 23h are moved into and out of the slots.

In order to rotatably mount the disc 68 carrying contact assembly 66 within the receptacle housing, the disc 68 is provided with a central opening 72 that is generally hexagonal shaped for receiving a sleeve-like shaft 74 having a portion 7S which is also hexagonal shaped. The remaining portions of the shaft 74 are cylindrical including reduced diameter portions along the shaft permitting independent rotation of the shaft and disc 68 in a manner to be described below. Disposed within the central opening 72 of shaft 74 is a shaft 76 which in the present instance includes at one end thereof a male contact 78 which engages with the central socket contact 38 in the plug. Disc 45 which carries the receptacle connectors 23 is secured to the central shaft 76 so as to be rotatable therewith.

Positioned on the cylindrical portion 80 of shaft 74 is a receptacle block 82 which carries a plurality of receptacle conductors 84 disposed in openings y86 of block 82. In order to secure the receptacle block 82 to housing 46, the block 82 is provided with a threaded skirt 88 which threadably engages with the internal threaded portion of the receptacle housing. In order to prevent relative rotation between the block 82 and housing 46, a pin 92 or the like extends through the housing into the skirt 88 of block 82.

In order to secure the shafts 74, 76 in the receptacle 16 yet enabling relative rotation therebetween, there is provided a retainer ring 94 nested in an annular groove formed in the cylindrical portion 80 of shaft 74. A bushing 96 surrounding the shaft 74 permits free rotation of the shaft 74 with respect to the receptacle block 82.

iFor the purpose of connecting the receptacle conductors -84 to the conductors of cable 20 (as best shown in FIG. 1), a plurality of terminal connectors 100 are provided, each of which includes a receptacle lug 102 bolted to the conductors 84 by suitable threaded fastener 104. Terminal clamps 106 secured to the lugs 102 by means of screws 108 or the like are provided to secure the conductors of cable 20 to the conductors 84.

With the conductor wires of cable 20 connected to the terminals 106 and with the cable wires connected to a suitable power source (not shown) the conductors 84 will be hot or electrically live connections; however, the contact assemblies 66 can be rotated into and out of the circuit with the conductors 84 to present an open circuit when the plug is inserted or withdrawn from the receptacle.

In accordance with yet another aspect of the invention, provision is made for substantially instantaneously completing or interrupting the circuit between the receptacle contacts 23 and the conductors 84 through the rotatable disc-carried contact assemblies 66, the respective contacting surfaces being engaged and disengaged with a minirnum possibility or arcing and with a greater assurance that smooth dependable contacting surfaces are brought into engagement. In carrying out this aspect of the invention there is provided a detent mechanism or the like generally indicated at 110 (FIGS. 1 and la) which interconnects the shafts 74, 76 so that rotation of the shaft 76 exerts a torque upon shaft 74, the latter being restrained for rotating during a portion of the rotational movement of shaft 76. After suflcient buildup of torque upon shaft 74 the shaft restraining means is triggered permitting the shaft 74, carrying disc 68 and contact assemblies 66 to snap into engagement with or disengagement from the receptacle contact lugs 23a and conductors 84 depending upon the direction in which the shaft 76 is rotated.

For details of the mechanism for accomplishing this, reference is made to the aforesaid copending U.S. application Ser. No. 527,625 led Dec. 2, 1965, now U.S. Patent 3,330,920. Briefly stated, the mechanism 110 includes an actuator 112 xed to shaft 74. The actuator 112 is generally triangular shaped with bent-over lugs or tangs 114-116 at the vertices. A torsion spring 118 with its coils disposed about bushing 96 surrounding shaft 74 and the ends 120, 121 of the spring 118 being crossed bear upon the lug 115 of actuator 112.

A disc actuator member 124 is secured to shaft 74 and is also of generally triangular shape having depending bent-over portions 126-128 at its vertices, with the bent-over portion 128 extending adjacent the lug 115 of actuator 112. A pair of trigger members 130, 132 are pivotally mounted on a pin 134 secured to the receptacle block 82 by a suitable bolt 135. The trigger members 130, 132 are oppositely oriented and biased towards one another by a torque spring 136y mounted on pin 134. Each of the trigger members is provided with a slot 138, 140, respectively, adapted to receive lugs 126, 127, respectively, on the disc actuator member 124. Shoulders 142, 143, on the outer ends of the trigger members 130, 132, respectively, are disposed in the paths of lugs 114, 116, respectively, of actuator 112 when itis rotated.

In order to more fully understand the mode of operation of the detent mechanism, as best shown in FIG. la the lug 126 of disc actuator member 124 is seated in the slot 138 of trigger member 130 which for the present purposes is considered to be the position where the contact assemblies 66 are in alignment with the receptacle contacts 23 and the conductors 84 and will be referred to herein as the on position.

It should be understood as the ensuing discussion proceeds that while four contacts are provided on both the receptacle and the plug wherein the circuit is to be opened and closed therebetween, there is no such limitation in actual practice, and the number of contacts is determined, as desired, by the number of conductors in the cables to be employed and the number of circuits to be completed. With the number of contacts selected as four in the description of the illustrative form of the present invention, the contacts are proportionately distributed with a center-to-center arcuate distance of approximately 45 degrees. Thus, the actautor member 112 is dimensioned such that rotation of shaft 76 in turn rotates the actuator bringing lug 114 into engagement with shoulder 142 of the trigger 130 in approximately 221/2 degrees of rotation. At this point, the lug 114 pushes against the shoulder 142 and during subsequent rotational movement of actuator 112 through another 221/2 degrees, the lug 126 is released from slot 138 in the trigger. Since there is a buildup of torque applied to the disc actuator 124 during the rst 221/2 degrees of rotation of actuator 112, when the lug 126 is released, the disc actuator 124 will snap in the same direction as actuator 112 is rotating and lug 127 will seat into slot 140 of trigger 132. The snap action of disc actuator 124, as previously described, rotates the shaft 74 so that contact assemblies 66 via their carrying disc 68 are moved out of engagement with the receptacle contacts 23 and the conductors 84, this position being called olf position. Rotation of the actuator 112 in the opposite direction brings lug 116 into engagement with the shoulder 143 of trigger member 132 releasing lug 127 of disc actuator 124 and'causing the disc actuator to snap in the other direction until lug 126 stops in slot 138 of trigger 130.

In accordance with still another important aspect of the present invention, provision is made for the inclusion of continuous connection of neutral circuit members and the like upon insertion of the plug into the receptacle regardless of Whether or not the connector includes open circuit contacts wherein the electrically live circuit may be interrupted subsequent to insertion and prior to withdrawal of the plug. To this end, referring to FIG. `l, cable connecting lug 146 is attached to central shaft 76 permitting utilizing the latter as a neutral circuit path between central receptacle contact 78 and the cable connecting lug 146. In order to permit relative rotation of the central shaft 76 with respect to the lug 146, connection therebetween is accomplished through use of a cylindrical pin 148 aflixed to the lug 146 with the pin being received in an axially extending bore 150 at the end of the shaft 76. For the purpose of connecting neutral cables or the like to lug 146 there is provided a terminal clamp 152, similar to clamps 106 which connect the hot conductors to the receptacle contact 84.

Since the central contact 38 of the plug remains in contact with receptacle contact 78 there is a continuous connection path afforded through the center of the connector which is unaffected by rotation of the plug, as in the case of the open circuit contacts herein.

In order to avoid damage to the receptacle contacts 23 and to prevent possible rotation of the receptacle contacts when the plug is removed, a protective disc 158 having openings through which the receptacle contacts can be made to extend, normally covers contacts 23. As best shown in FIGS. 1 and 8, the protective disc is normally urged outwardly by spring 160l interposed between the receptacle disc 45 and the protective disc. When the plug is inserted in the receptacle it bears against the disc 158 to compress the spring 160 thereby allowing receptacle contacts 23 to protrude through the disc 158 openings and engage corresponding socket connectors 22 of the plug. VJhen the plug is withdrawn, the protective disc moves forward under the action of the spring 160 and the receptacle contacts 23 are safely hidden behind the disc 158, as shown in FIG. 8.

In accordance with yet another feature of the present invention, provision is made for preventing unauthorized or accidental removal of the plug from the receptacle which also allows the plug to be locked to the receptacle with or without preventing movement between an open contact and a closed contact position. To this end, referring to FIGS. l, 2, and 7, conjointly, radially inwardly extending pins 162, 164 on the inner surface of the receptacle sleeve 46 and the inner surface of the rotatable collar 52, respectively, cooperate with polarizing slots 166 in the outer surface of the plug housing 26 (FIG. 7)

to assure orientation of the plug for insertion into the receptacle. Pins 162, 164 are in axial alignment when the plug is inserted into the receptacle and in order to prevent the plug from lbeing withdrawn after it is cornpletely inserted into the receptacle, circumferentially extending leg portions 168 of polarizing slots 166 receive pins 164 of the collar 52 upon rotation of the latter. In order to permit the plug to be rotated for actuating detent mechanism 110 after it has been completely inserted, the polarizing slots 166 are formed with other circumferentially extending leg portions 170 which are engaged by pins 162. Explosion-proof withdrawal of the plug is assured as it first must be rotated to remove the pins 162 from the leg portions 170 whereupon the contacts are separated in the manner previously described and the collar 52 must be rotated to bring pins 164 out of leg portions 168 into alignment with pins 162 along the polarizing slot 166.

In order to prevent unauthorized tampering with the connector, locking means 172, as viewed in FIGS. 2, 3, and 4, may be provided to receive a seal or lock thereby preventing the collar 52 from being rotated. In the present instance, the locking means 172 includes an arm 174 projecting outwardly from the collar 52 and having an aperture adjacent its outer end. A second arm 176 projecting from the receptacle housing 46 includes an aperture that becomes aligned with the aperture in arm 174 when, for example, the collar 52 is rotated to a position as shown in FIG. 2. A locking device (not shown) may be inserted through the apertures of arms 172, 174 to maintain the pin 164 out of alignment with pin 162 thereby preventing removal of the plug from the receptacle.

In the illustrative embodiment as shown, the collar 52 is rotated to bring pins 164 out of alignment with pins 162 on the receptacle housing with the arrangement being such that the locking means 172 can be locked to prevent removal of the plug, yet it permits the plug to be rotated to open and close the circuit between the receptacle and plug contacts. It will be apparent, however, that the locking means toegther with the leg portions 168 of polarizing slot 166 can be so arranged that the plug can be locked in either the on or ofi position in addition to preventing withdrawal of the plug from the receptacle.

In order to more fully explain the mode of operation of the present invention, reference is now made to FIGS. 9 through 12, inclusive, where illustrative diagrams showing the positioning stages of the plug and receptacle contact members are shown. Turning first to FIG. 9 the electrical connector is shown in the off position such as when the plug is first completely inserted in the receptacle. The contact assemblies 66, together with the disc 68 are approximately 45 degrees out of alignment from the hot cont-acts 84. 'I'he generally kidney-shaped plug contact portions 23b also may not engage the contact assemblies 66 when the plug is first inserted into the receptacle and the circuit between the plug and the receptacle still remains open. When the plug is rotated a first 221/2 degrees, as herein shown in FIG. 10, the receptacle contacts 23 and disc 45 moves so that the kidney-shaped portions 23b of the receptacle contacts enter slots 69 of contact assemblies 66. Since the disc 68 is restrained contact portions 23b fully enter the slots 69, however, there is still no connection with the hot conductors 84 and the circuit remains open. Continued rotation of the plug through a subsequent 221/2 degrees triggers the disc 68 carrying the contact assemblies 66 as previously described, whereby contact assemblies 66 slide along the surface of contact portions 23b and contact surfaces defined by slots 70 slide into engagement with the hot conductors 84 completing the circuit at the end of 45 degrees of travel of the plug, as shown in FIG. 11. Since contact assemblies 66 slide into engagement with the conductors 84, and also, slide -along the surface of neceptacle contact portions 23b there is little likelihood of arcing occurring between the contacts, and they are substantially self-cleaning for smooth, dependable operation.

When the plug is to be removed from the receptacle, rotating the plug, as herein shown in FIG. 12, during the first 221/2 degrees, the receptacle contact portions 23b slide along contact assemblies 66, yet the circuit remains closed. During the second 221/2 degrees of rotation of the plug, the disc-carried contact assemblies 66 are triggered and return again to the position shown in FIG. 9.

The kidney-shaped receptacle Contact portions 23b insure that the receptacle contacts always remain in engagement with the disc assemblies 66 as the plug is rotated to the off position. Thus, the circuit is broken only when the contact assemblies 66 snap out of engagement with conductors 84 and any arc which might occur will be contained within the sealed receptacle body. Since the plug cannot be removed from the receptacle until the circuit is opened, there is no chance of causing a chain-type explosive reaction in the presence of highly explosive atmospheres.

Referring to FIG. 13, a slightly modified form of an explosion-proof plug and receptacle, generally indicated at 14A and 16A, respectively, has been depicted, but which also embodies certain of the features of theV connector in FIG. 1. The general construction of the plug and receptacle is similar to that shown in FIG. 1, therefore corresponding reference numerals have been employed with the subscript A to represent corresponding parts.

In the present instance, the receptacle conductors 84A extend through openings 84A in block 82A, generally in alignment with corresponding receptacle contacts 23B on the rotatable disc 45A. In order to open and close the circuit between conductors 84A and contacts 23B there is, in this instance, provided a plurality of bridging contact members 66A carried by a rotatable disc rnember 68A. The contact mem-bers 66A are in the form of cylinders (FIG. 14) rotatably seated on inserts 182 disposed in grooves about the periphery of disc 68A and urged outwardly by springs 184. The cylinders are held in place by a retaining member surrounding the disc 68A at approximately the center of the disc 68A. Grooves 186 formed in the inner peripheral edge of the retaining member 180 hold the cylinder 66A in place and permit the cylinders 66A to rotate within their seats.

Thus, when disc 68A is rotated, opposite end portions of cylinders 66A are brought into and out of contact with respective aligned pairs of conductors 84A and contacts 23B with a combined rolling and sliding action. Since there is this ability to permit the contact cylinders 66A to rotate within their seats, a longer wearing life over repeated make and break actions is assured.

I claim as my invention:

1. In an electrical connector adaptable for explosionproof use, the combination comprising, a plug having a generally tubular casing including a sleeve-like extension at one end thereof, an insulator block mounted within said plug casing having a plurality of, circumferentially spaced contacts recessed therein, a receptacle having a generally tubular sleeve-like body and means adapted t0 telescopically receive said plug extension, disc means rotatably mounted in said receptacle body, said disc means carrying a plurality of circumferentially spaced contacts having first and second contacting elements, said first elements engaging with said plug contacts upon insertion of said plug into said receptacle, a rotatable disc mounted in said receptacle body, said rotatable disc carrying a plurality of circumferentially spaced contact members having first and second contacting surfaces, a plurality of circumferentially spaced receptacle conductors mounted in said receptacle body for electrical engagement with said second contacting surfaces of said rotatable disc upon rotation of the latter into alignment therewith, actuating means connected to said disc means and said rotatable disc for rotationally snapping said contact members into and out of engagement with said receptacle conductors and the second contacting element of said disc means, and means coupling said actuating means and said disc means so that rotation of said plug when inserted within the receptacle rotates said disc means therewith operating said actuating means.

2. The combination as defined in claim 1 further characterized by said plug contacts being female contacts and said contacts of said disc means being male contacts.

3. The combination according to claim 2 wherein said receptacle includes a protective disc, said protective disc having openings adapted to receive said male contacting elements and axially shiftable with respect thereto between an inwardly disposed position wherein said male contacts are exposed and an outwardly disposed position wherein said male contacts are hidden behind said protective disc and spring means for normally urging said protective disc outwardly when said plug is removed from the receptacle.

4. The combination as defined in claim 1 further characterized by said second contacting elements of said disc means including arcuate enlarged portions adjacent their ends, said portions being generally kidney-shaped in crosssection and disposed in the path of rotation of respective ones of said first contacting surfaces of said rotatable disc for electrical engagement between said first surfaces and said portions upon rota-tion of the disc and said enlarged portions of the second contacting elements being dimensioned so that said portions and said first contacting surfaces are in engagement at least prior to and until after said second contacting surfaces and said conductors are brought into and out f engagement, respectively, upon rotation of said rotatable disc.

5. The combination as defined in claim 4 further characterized by said contact members of said rotatable disc each comprising at least a pair of resilient contact elements, secured to one another intermediate their ends, the adjacent ends of said resilient elements being arcuate and spaced from one another so as to define a slot therebetween, and said receptacle conductors being received in respective ones of the slots upon rotation of the rotatable disc contact members into alignment therewith.

6. The combination as defined in claim 4 further characterized by said contact members of said rotatable disc being in the form of cylinders rotatably mounted in fixed positions about the periphery of said rotatable disc and the peripheral opposite end portions of said cylinders defining said rst and second contacting surfaces.

7. The combination as claimed in claim 1 wherein said plug includes a contact element centrally disposed with respect to the axis thereof, said receptacle includes a contact element centrally disposed with respect to its axis for engagement with said centrally disposed plug contact element and means including a central shaft mounted in said receptacle and coupling said disc means to said actuating means, said central shaft means providing a continuous neutral circuit path between said plug and receptacle central contact element upon insertion of the plug within the receptacle.

8. In an electrical connector adaptable for explosionproof use, the combination comprising, a plug having a generally tubular casing, an insulator block mounted within said plug casing having a plurality of circumferentially spaced contacts therein, a receptacle having a generally tubular body and means adapted to telescopically receive said plug, insulating means mounted in said receptacle body, said insulating means carrying a plurality of circumferentially spaced contacts having first and second contacting elements, said first contacting elements engaging with said plug contacts upon insertion of said plug into said receptacle, an insulating disc rotatably mounted in said receptacle body, said disc carrying a plurality of circumferentially spaced contact members having first and second contacting surfaces, a plurality of circumferential- 1y spaced receptacle conductors mounted in said receptacle body for electrical engagement with said second contacting surfaces of said disc upon rotation of the latter, said disc contact members being normally out of engagement with said receptacle conductors and said second contacting elements of said insulating means when the plug and receptacle are separated, actuating means connected to said disc for rotationally snapping said disc carried contact members into and out of engagement with said receptacle conductors and the second contacting elements of said insulating means, means carried by said receptacle for operating said actuating means to rotate said disc carried contact members into engagement with said conductors and said contacting elements only when said plug is inserted within the receptacle and means for preventing removal of said plug from the receptacle until said disc carried contact members are out of engagement with said receptacle conductor and said second contacting elements.

9. The combination as claimed in claim 8 wherein said plug contacts are female contacts and said receptacle contacts are male contacts.

10. An electrical connector as claimed in claim 8 wherein said plug removal preventing means comprises polarizing means including a pin extending in front of the inner surface of said receptacle body and an axially extending slot and transversely extending leg portion on the outer surface of said plug casing for guiding said plug for axial insertion into said receptacle and for subsequent rotation thereof, a retaining structure comprising a collar rotably mounted on the end of said receptacle body, a pin mounted on the inner surface of said collar so that said collar pin may be axially aligned with said receptacle body when the plug is inserted into the receptacle and a transversely extending slot on said plug casing surface interconnecting said axially extending slot and aligned with said collar pin when Athe plug is inserted into the receptacle, said transverse slot being dimensioned so that when said collar is rotated with the plug inserted into the receptacle, said pins are out of alignment thereby preventing removal of the plug from the receptacle.

11. An electrical connector comprising, in combination, a plug having a plurality of circumferentially spaced female contacts, a receptacle adapted to be connected to a source of current, carrying means in said receptacle for carrying a plurality of circumferentially spaced male contacts which engage with said plug contacts upon insertion of said plug into said receptacle, means for inserting and rotating said plug in said receptacle, switching means disposed within said receptacle for opening and closing a circuit between the current source and said receptacle contacts, said switching means having a first position so that the circuit is normally open when the plug and receptacle are separated, means connected to said receptacle male contact carrying means for operating said switching means effecting a second position wherein the current is closed only when said plug is inserted within the receptacle and rotated, means carried by said receptacle male contact carrying means operative upon disconnection of said plug and receptacle for hiding said male contacts and preventing rotation of said receptacle male contact carrying means, and means for preventing removal of said plug from the receptacle until said switching means is returned to the normally open circuit first position.

12. In an electrical connector arrangement including a cable having a first end adapted for connection with an electrical load with a second end having a plug connected thereto, the improvement comprising, said plug including female contacts, a receptacle adapted for electrical connection with a source of power and having means carrying male contacts for electrical connection with said plug, switch means disposed within said receptacle and electrically interposed between said male contacts and the source of electrical power, means whereby said switch means operates upon rotation of said male contact carrying means, and protective means operable upon disconnection of said plug and receptacle for hiding said male 5 12 References Cited UNITED STATES PATENTS 8/ 1930 Fagerlund 200-51 2/1913 Knauff 20D-51.09 

